Low-dose Gamma Irradiation and Refrigerated FStorage in vacua Affect Microbial Flora of Fresh Pork

Vacuum-packaged ground fresh pork samples absorbed gamma radiation doses of 0. 0.57. 1.91. 3.76. 5.52. or 7.25 kGv at 2°C. Samolcs were analyzed after 1, 7, 14, 21, 28,‘or 35 days itorage at 2°C’for presence and number of aerobic and anaerobic mesophiles and endospore formers, and aerobic psychrotrophs. Conventional plate counts did not detect surviving microflora in any sample that received an absorbed dose of 1.91 kGy or higher, even after refrigerated storage for up to 35 days. The microflora in the control were predominantly Gram-positive for the first 21 days; however, Serratia predominated at 28 and 35 days. Staphylococcus, Micrococcus, and yeast species predominated in samples that received 0.57 kGy.     

Water Concentration/Activity and Loss of Vitamins B1 and E in Pork Due to Gamma Radiation

When irradiated, increasing the water content of pork by partial rehydration of freeze-dried L. dorsi muscle resulted in increasing rate of thiamin loss from zero in dry tissue to ca 6%/kGy of irradiation in tissue with 70% water. Conversely, the rate of loss of α-tocopherol decreased, from 44%/kGy at 0% to 32%/kGy at 70% water. Decreasing water activity in buffers or in ground or freeze-dried pork by salt or sucrose had no effect on rate of loss of either vitamin following irradiation. Salt decreased the loss of both vitamins in pork due to competition for the hydroxyl radical by chloride ions.     

Gamma Irradiation Effects on Thiamin and Riboflavin in Beef, Lamb, Pork, and Turkey

A study was made of the loss of thiamin and riboflavin due to gamma irradiation of beef, lamb and pork longissimus dorsi, turkey breast and leg muscles. Thiamin losses averaged 11%/kiloGray (kGy) and riboflavin losses 2.5%kGy above three kGy. The rate of loss of thiamin in beef was higher than that in lamb, pork and turkey leg, but not turkey breast. with losses of 16%/kGy in beef and 8%/kGy in lamb. The rate of thiamin loss was not related to sulfhydryl, protein, moisture, fat or water content, pH or reducing capacity by redox titration. Loss of riboflavin was not different among species. Any detriment from such slight losses would seem to be more than compensated by the advantage of controlling bacteriological contamination by irradiation processing.     

Quality properties of sausage made with gamma-irradiated natural pork and lamb casing

Quality properties in emulsion-type sausage stuffed into irradiated natural casing were studied. Fresh salted and semidried natural pork and lamb casing was washed and irradiated at 0, 3, and 5 kGy by gamma-ray and emulsion-type pork sausage (Brattella Weiss Wurst) was manufactured. The sausage was stored in a 4°C refrigerator. The numbers of total aerobic bacteria, Enterococcus and coliform bacteria in the irradiated natural casing or sausage prepared from irradiated casing were significantly decreased or eliminated compared to those of the nonirradiated control. The D(10) values of total aerobic bacteria of the pork and lamb casing were 0.87 and 0.92 kGy, respectively. The vacuum-packaged sausages made with irradiated casings had a higher 2-thiobarbituric acid reactive substances value than that of the nonirradiated controls only at 5-day with pork casing and at 10-day with lamb casing. The total working force for shear of the sausages was decreased in both irradiated casings but the sensory evaluation showed no difference. Therefore, the gamma irradiation was a useful technique to sanitize the natural pork and lamb casings and to extend shelf-life, primarily microbial quality, of the sausage made with natural casings.     

Irradiation inactivation of Listeria monocytogenes in low-fat ground pork at freezing and refrigeration temperatures

Gamma radiation effectively controls Listeria monocytogenes in uncooked and in ready-to-eat foods. This study was conducted to determine if gamma radiation could be used to control L. monocytogenes in ground pork. Ground pork was contaminated with L. monocytogenes, kept at refrigeration (4 degrees C), chilling (0 degrees C), and freezing (-18 degrees C) temperatures overnight, exposed to gamma radiation and stored at 4 degrees C for 7 days, and at 0 and -18 degrees C for 60 days. Following irradiation, the meat was assayed for L. monocytogenes viable counts and lipid oxidation. A triangle test was performed to determine if sausage made from the irradiated and nonirradiated ground pork differed in sensory quality. It was observed that a 5-log reduction of L. monocytogenes viable counts would require a 3.0-kGy radiation dose. The results of a 60-day storage study of ground pork inoculated with 10(5) to 10(6) CFU of L. monocytogenes per gram indicated that counts for nonirradiated meat remained fairly constant at refrigeration, chilling, and freezing temperatures. However, irradiation of ground pork at 3.0 kGy could inactivate L. monocytogenes totally in ground pork subsequently held at all the temperatures used in this study. Lipid oxidation measurements, as determined by the thiobarbituric acid-reactive substance assay, ranged from 0.16 nmol/g for nonirradiated ground pork and 0.20 nmol/g for meat irradiated at 3.0 kGy. Sensory panelists could distinguish between irradiated and nonirradiated sausage but were divided on whether irradiation adversely affected the sausage quality. Our results suggest that gamma radiation could be useful to control L. monocytogenes in ground pork and improve the safety of ground pork products.     

Volatile production in irradiated normal, pale soft exudative (PSE) and dark firm dry (DFD) pork under different packaging and storage conditions

Normal, pale soft exudative (PSE) and dark firm dry (DFD) pork Longissimus dorsi muscles were vacuum packaged, irradiated at 0 or 4.5 kGy and stored at 4°C for 10 days. Volatile production from pork loins was determined at Day 0 and Day 10 of storage at 4°C. With both aerobic and vacuum packaging, irradiation increased the production of sulfur-containing volatiles (carbon disulfide, mercaptomethane, dimethyl sulfide, methyl thioacetate and dimethyl disulfide) in all three pork conditions at Day 0 but did not increase hexanal – the major indicator volatile of lipid oxidation. The PSE pork produced the lowest amount of total sulfur-containing volatiles in both aerobically and vacuum-packaged pork at Day 0. The majority of sulfur-containing volatiles produced in meat by irradiation disappeared during the 10-day storage period under aerobic packaging conditions. With vacuum packaging, however, all the volatiles produced by irradiation remained in the packaging bag during storage. Irradiation had no relationship with lipid oxidation-related volatiles (e.g. hexanal) in both aerobic and vacuum-packaged raw pork. The DFD muscle was very stable and resistant to oxidative changes in both irradiated and nonirradiated pork during storage, suggesting that irradiation can significantly increase the utilization of raw DFD pork and greatly benefit the pork industry.     

Identification of Microbial Isolates from Vacuum-Packaged Ground Pork Irradiated at 1 kGy

Bacterial cultures from irradiated (1 kGy) and nonirradiated, vacuum-packaged ground pork held at 5°C were isolated and characterized over a 12-day storage period. The initial flora of the meat was composed mostly of Pseudomonas sp. and Enterobacter sp. Although the microflora of nonirradiated samples gradually shifted from Gram-negative to Gram-positive microorganisms, 76% of the isolates were characterized as Gram-negative at the onset of spoilage (9 days at 5°C). In contrast, the irradiated ground pork microflora was mainly Gram-positive (66%) shortly after irradiation and increased to 97% after 9 days at 5°C. A total of 720 isolates were identified to genus.     

Changes of colour and pH in fish musculature after ionizing radiation exposure

Irradiation of meat causes sensory changes as do other technological methods. The most significant sensory and quality indicator of meat is colour; therefore, the effect of irradiated pieces of fish was studied in relation to colour changes. Colour was measured at the musculature of Oncorhynchus mykiss. The parameters of colour, L*, a* and b*, were determined with the portable Superchroma S-Spex (Braive) spectrophotometer in the CIELAB system before irradiation (3 h post mortem) and after irradiation (⁶⁰Co source, a dose of 3 kGy and a dose rate of 3.33 kGy h^–1) (5 h post mortem). The change of L* was identical for both irradiated and nonirradiated samples. This change may be caused by maturation of fish flesh. a* was identical and b* decreased. This effect differs from that of irradiated pork. The decrease of the pH was identical for both irradiated and nonirradiated samples. This change may be caused by maturation of fish flesh.     

Color changes in irradiated cooked pork sausage with different fat sources and packaging during storage

Pork sausages were prepared with lean pork meat, fat from different sources [backfat (BF), corn oil (CO) or flaxseed oil (FO); 10% of lean meat], NaCl (2%), and ice water (10%). The emulsified meat batters were stuffed into casings (3 cm in diameter) and cooked to an internal temperature of 72°C. Cooked sausages were sliced and vacuum- or aerobic-packaged individually. Sausages were irradiated at a 0, 2.5, or 4.5 kGy dose and stored in a 4°C refrigerator for 8 days. Aerobic-packaged, irradiated cooked sausages prepared with BF and FO showed higher Hunter L-values than nonirradiated controls at day 0, but the difference disappeared at day 8. Irradiation increased the Hunter a-value in vacuum-packaged cooked pork sausages regardless of the fat source used, and the increase of the Hunter a-value was dose-dependent. In contrast, the Hunter a-value decreased by irradiation in aerobic-packaged cooked pork sausages prepared with BF or FO. The Hunter a-value of cooked pork sausage with aerobic packaging was significantly reduced at day 8. Hunter b-values increased at Day 8 in irradiated cooked pork sausages except for the sausage prepared with CO at 2.5 kGy. Cooked pork sausages prepared with CO were lighter, and sausage prepared with FO was redder and more yellow (p<0.05) in vacuum packaging.     

Validation of an alternative method for the identification of 2-dodecylcyclebutanone (2-DCB) of irradiated meats by solid-phase microextraction (SPME) gas chromatography–mass spectrometry (GC-MS)

A rapid and simple procedure to detect irradiated food containing fat is proposed. This method is based on HS-SPME coupled with GC-MS to determine the presence of a radiolytic product in irradiated meats: 2-dodecylcyclobutanone (2-DCB) and is proposed as an alternative to EN 1785:2003, which is a long and complex procedure. The qualitative confirmation method is validated on different type of meats: chicken, turkey, duck, beef, pork on both nonirradiated and irradiated samples at different dose levels (0.05, 0.12, 0.5, 1.0 and 3.0 kGy) with a biological X-ray irradiator. The validation parameters investigated are selectivity, minimum dose level (MDL), limit of detection (LOD), sensitivity and specificity. The MDL and LOD values were 0.5 kGy and 5.0 ng mL⁻¹, respectively, for all matrices. No false positives or false negatives occurred, and 100% of samples were correctly identified. The results show that HS-SPME GC-MS is suitable for routine analysis.     

Lipid oxidation, color changes and volatiles production in irradiated pork sausage with different fat content and packaging during storage

Effects of irradiation on lipid oxidation, color and volatiles production in pork sausages with different fat content and packaging were determined. Sausages (with 4.7, 10.5 and 15.8% fat content) were sliced and vacuum-packaged either in oxygen-permeable or impermeable bags, irradiated (0 or 4.5 kGy) and stored at 4°C for 7 days. Lipid oxidation, color and volatiles productions were analyzed at 0, 3 and 7 days of storage. TBARS (2-thiobarbituric acid reactive substances) values of cooked pork sausages increased with the increase of fat content regardless of storage, irradiation or packaging types. Irradiated samples had higher TBARS than nonirradiated at 0 day but the difference disappeared during storage in both packaging types. Lightness of sausages (Hunter L-value) increased with the increase of fat content and storage time but was not affected by irradiation. In aerobic packaging, irradiation reduced Hunter a-values of pork sausages at 0 day but irradiation effect on a-value disappeared during storage. In vacuum packaging, however, irradiated samples had higher Hunter a-values than nonirradiated samples. Irradiation increased 1-heptene and total volatiles, but the amount of 1-heptene was not associated well with TBARS values of pork sausages. In both irradiated and nonirradiated pork sausages, aerobic packaging produced more volatiles than vacuum packaging during storage. It was concluded that irradiation and fat content had significant effects on lipid oxidation, color and volatiles production of cooked pork sausages during storage but that oxygen availability had a stronger effect than irradiation and fat content.     

Retention of quality and nutritional value of 13 fresh-cut vegetables treated with low-dose radiation

Improving the microbial safety while maintaining quality of fresh fruits and vegetables will increase consumer confidence in fresh produce. This study was conducted to investigate the effects of irradiation at 1 kGy, a dose that potentially inactivates E. coli O157:H7 by 5 logs, on the quality of 13 common fresh-cut vegetables: iceberg, romaine, green and red leaf lettuce, spinach, tomato, cilantro, parsley, green onion, carrot, broccoli, red cabbage, and celery. The results showed that the appearance of irradiated samples was similar to the nonirradiated ones except that irradiated carrots, celery, cilantro, and green onions had higher appearance scores than corresponding nonirradiated vegetables. There was no difference in the instrumental texture between irradiated samples and nonirradiated ones. The aroma of several irradiated vegetables was significantly better than controls after 14-d storage, because these control samples decayed or senesced. The 1 kGy irradiation did not affect vitamin C content of most vegetables; however, irradiated green and red leaf lettuce had 24% to 53% lower vitamin C contents than the controls. Our results suggest that most fresh-cut fruits and vegetables tested can tolerate up to 1 kGy irradiation without significant losses in any of the quality attributes.     

Analysis of volatile components and the sensory characteristics of irradiated raw pork

Longissimus dorsi muscle strips, approximately 20 mm long, 40 mm wide, and 5 mm thick (4 g), of pig were randomly placed in a single layer into labeled bags (four strips per bag) and packaged either aerobically or under vacuum. Samples in the bags were irradiated at 0, 5, or 10 kGy and stored at 4°C for 5 days. Lipid oxidation, the amount and identity of volatile components and sensory characteristics of raw pork strips were determined at 0 and 5 days of storage. Irradiated muscle strips produced more 2-thiobarbituric acid reactive substances (TBARS) than nonirradiated only in aerobic packaging during storage. Irradiation had no effect on the production of volatiles related to lipid oxidation, but produced a few sulfur-containing compounds not found in nonirradiated meat. This indicates that the major contributor of off-odor in irradiated meat is not lipid oxidation, but radiolytic breakdown of sulfur-containing amino acids. Many of the irradiation-dependent volatiles reduced to 50 to 25% levels during the 5-days storage under aerobic conditions. Irradiated muscle strips produced stronger irradiation odor than nonirradiated, but no irradiation dose or storage effect was found. Irradiation had no negative effect on the acceptance of meat, and approximately 70% of sensory panels characterized irradiation odor as barbecued-corn-like odor.     

Lipid Oxidation, Volatiles and Color Changes of Irradiated Pork Patties Affected by Antioxidants

Changes were measured in TBARS, color, and volatiles of irradiated (4.5 kGy) pork patties with antioxidants (sesamol, quercetin, rutin, BHT, and rosemary oleoresin) during 7 days storage at 4°C. Irradiation accelerated lipid oxidation of raw pork during storage. However, irradiation before cooking did not influence lipid oxidation of cooked pork during storage. Sesamol, quercetin, and BHT were effective in both irradiated raw and cooked pork during 7-days storage. Rosemary oleoresin and rutin were effective only in irradiated raw pork for 3 days. Hexanal, propanal and higher boiling components were well correlated (P < 0.01) with TBARS in cooked pork. Generation of volatiles was reduced by sesamol and quercetin, but the effects of antioxidants on color changes of raw pork patties were minor and inconsistent.     

Functional properties of raw and cooked pork patties with added irradiated, freeze-dried green tea leaf extract powder during storage at 4 °C

Functional and sensory properties of raw and cooked pork patties with added irradiated freeze-dried green tea leaf extract powder were studied. Components of green tea were extracted by 70% ethanol, and the extract was irradiated to obtain a bright color. The irradiated green tea extract was freeze-dried and the powdered sample (0.1%) was added to the pork patties (Trt C). Pork patties without any ingredient (Trt A) and with nonirradiated, freeze-dried green tea extract powder (Trt B) were also prepared for comparison. Lipid oxidation, radical scavenging effect, color, and sensory properties of pork patties with treatments were analyzed at 5-day intervals for 15 days with storage at 4?°C. The lipid oxidation had a lower (P<0.05) and radical scavenging effect was greater (P<0.05) in the raw and cooked pork patties with added Trt B and Trt C, than those of Trt A (control). The pork patties with Trt B and Trt C had a higher Hunter color a*-value and less cooking loss than that of Trt A. Sensory panelists preferred the odor of the raw pork patties and color of the cooked pork patties of Trt C (P<0.05). Generally, no significant difference between Trt B and Trt C was found. Therefore, irradiated, freeze-dried green tea extract powder can be used for producing functionally-improved meat products.     

Effect of irradiation and modified atmosphere packaging on the microbiological and sensory quality of pork stored at refrigeration temperatures

The effect of combining low-dose irradiation (1.75 kGy) with modified atmosphere packaging (MAP) on the microbiological and sensory quality of pork chops stored at refrigeration temperatures was studied. The microflora of irradiated MAP pork was almost exclusively composed of lactic acid bacteria, predominantly Lactobacillus spp. Modified atmospheres containing either 25 or 50% CO₂, balance N₂, resulted in the best microbial control in irradiated pork held at 4°C, compared to an unirradiated MAP control, and these atmospheres were subsequently used in sensory studies. The atmosphere containing 25% CO₂ 75% N₂ maintained the uncooked colour and odour of irradiated pork chops more effectively than 50% CO₂ 50% N₂. Therefore packaging in a modified atmosphere containing 25% CO₂, balance N₂, followed by irradiation to a dose of 1.75 kGy is recommended to improve the microbiological and sensory quality of pork chops.     

Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production, and color in raw pork patties

Effects of packaging and irradiation combinations on lipid oxidation, off-flavor, and color changes of raw patties prepared from three pork muscles were studied. Patties were prepared from each of the ground L. dorsi (L. thoracis and lumborum), psoas, and R. femoris muscles of pig, packaged either in oxygen permeable polyethylene bags or impermeable nylon/polyethylene bags, irradiated with an electron beam at 0 or 4.5 kGy dose, and then stored up to two weeks at 4 °C. Lipid 8 oxidation and color of the patties were determined after 0, 3, 7, and 14 days of storage, and volatiles 24 hr after irradiation. Irradiation and high fat content accelerated the lipid oxidation in raw meat during storage. Oxygen availability during storage, however, was more important than irradiation on the lipid oxidation and color values of raw patties. Irradiated meat produced more volatiles than nonirradiated patties, and the proportion of volatiles varied by the packaging-irradiation conditions of patties. Irradiation produced many unidentified volatiles that could be responsible for the off-odor in irradiated raw meat. No single volatile components but total volatiles, however, could be used to predict lipid oxidation status of raw meat.     

Sensory Analysis and Consumer Acceptance of Irradiated Boneless Pork Chops

Flavor, texture, and aroma were determined for chilled (3 ± 2°C) and frozen (–17 ± 3°C) boneless pork chops packaged in vacuum or air and exposed to an absorbed dose of 0, 1.5, or 2.5 kGy (chilled) or 0, 2.5, or 3.85 kGy (frozen) of electron beam and cobalt⁶⁰ irradiation. Irradiation (< 3.85 kGy) had minimal effects on aroma, flavor, and textural attributes in chilled and frozen boneless pork chops. Irradiation source had limited effects and packaging type had the greatest influence. Consumers reported no difference (P>0.05) between irradiated (2.5 kGy cobalt⁶⁰ irradiated, chilled, vacuum-packaged, boneless, pork chops) and control samples for overall acceptance, meatiness, freshness, tenderness and juiciness.     

Microbiological Method to Identify Irradiated Meat

Beef, chicken, mutton and pork exposed to -γ-radiation doses of 0–5 kGy were inoculated with Aeromonas hydrophila initially, after 7 days and 15 days of storage at 3°C and -11°C. After 18 hr incubation at 30°C TVBN values of nonirradiated samples were found to be 210 mg% and TVA value were 205 while the corresponding irradiated samples showed 30–80 mg% and 40–80. A similar pattern was observed in stored samples. A rapid method was developed by incubating chicken meat at 37°C for 6–7 hr with bacteria followed by estimation of volatile acids (TVA) and bases (TVBN). A 40–50% reduction in TVA and TVBN in irradiated samples was observed suggesting its possible application for detecting irradiated meat samples.     

Sensorial and chemical quality of gamma-irradiated fresh-cut iceberg lettuce in modified atmosphere packages

A study was conducted to investigate the effects of various doses of irradiation on the quality of fresh-cut iceberg lettuce and to determine a suitable maximum dose. Fresh-cut iceberg lettuce packaged in film bags was exposed to 0, 1, 2, 3, and 4 kGy of gamma radiation and stored at 3 degrees C for 14 days. CO2 levels were higher and O2 levels were lower in packages containing irradiated lettuce than in those containing nonirradiated lettuce for most of the storage period. Comparison with nonirradiated lettuce indicated that total ascorbic acid (ascorbic acid plus dehydroascorbic acid) content and firmness were not significantly influenced by irradiation at 1 or 2 kGy. The overall visual appearance was best for lettuce irradiated at 1 or 2 kGy. This improved quality may be related to the high CO2 and low O2 levels observed for the irradiated samples. Electrolyte leakage for lettuce increased with higher radiation doses and was correlated (R2 = 0.99) with a soggy appearance. The leakage for lettuce irradiated at > or = 2 kGy was significantly more extensive than that for nonirradiated lettuce. The irradiation of fresh-cut lettuce in modified atmosphere packages at doses of 1 kGy and perhaps 2 kGy for safety enhancement and quality improvement is feasible.